This invention relates to improvements to the Interactive Television and Data Transmission System technology which this inventor calls T-NET and which is described in detail in his U.S. Pat. No. 4,750,036 dated Jun. 7, 1988 and divisional U.S. Pat. No. 5,177,604 dated Jan. 5, 1993. T-NET provides bi-directional communication (either wireless or cable) from one or several central locations to a plurality of fixed or mobile subscriber transceivers throughout a metropolitan area for applications in interactive TV, 2-way data or voice transmission, and the like. Today, such systems are often referred to as interactive TV or multimedia delivery systems. Furthermore, many CATV (Cable TV) operators are desirous of adding telephone and portable (cordless) phone message delivery capability to their CATV systems.
Generally speaking, the related T-NET technology disclosed in the inventor's previous patents concern TV signal-compatible modulation methods wherein data signals to be transmitted downlink to subscribers or uplink from them are placed either: (a) in blanking intervals of a co-channel or adjacent channel "host" television signal or alternatively, (b) the effective polarity of the information is reversed on sequential host TV signal frames and superimposed upon it so as to thereby become invisible to its viewers even though transmitting co-channel. The inventor calls method (b) "dam-over-video".
Other related technology disclosed in aforesaid patents concern partitioning a metropolitan T-NET wireless service area into angular sectors and range intervals in a manner the inventor calls "virtual cellular" so as to gain the advantage of frequency re-use in non-adjacent cells to achieve substantially improved spectrum efficiency. This is made possible because T-NET measures and employs the RF signal propagation time to establish a radio "fence" (using "range gates") surrounding each transmitting device and thereby eliminates RF cross-talk between devices. This is in effect a combination of time-division and space division multiplex (TDM/SDM). A related method the inventor calls "cellular cable" is taught in the instant application.
Yet another related T-NET method disclosed in prior applications is "synergistic modulation" wherein data signals to be communicated to remote locations are superimposed upon another existing but unrelated local (host) signal transmission in such a manner so as to synergistically employ the carrier and some of the spectral or temporal modulation of the unrelated signal. In this method the remote T-NET receivers are designed to detect both the data and unrelated host signal and subsequently processes the received data signal as if it were a subcarrier of the unrelated host carder signal. This significantly improves the transmission reliability and detectability of the data in the presence of the usually more powerful unrelated signal, while minimizing or eliminating any interference the data might otherwise cause the unrelated signal, even when aforesaid data and host transmissions occur co-channel, or are on adjacent channels, or when the data and unrelated host signals propagate in opposite directions.
The application of the improved technology taught herein to interactive television and multimedia is of great interest today in the United States and elsewhere in the world. Improved use of the presently assigned radio frequency spectrum without displacing existing users, and more efficient and expanded use of existing telecommunication facilities are principal objects of this invention. Additional derailed background relating to the instant invention may be found in the patents cited above.